1. Field of the Invention
The present invention relates to a nonionic emulsifier which is used for emulsifying an asphalt and to an oil-in-water asphalt emulsion which is obtained by using the nonionic emulsifier and which has excellent stability in a stationary state and storability.
2. Prior Art
Heretofore, an asphalt has been used in a wide range of applications, for example, an asphalt pavement, an water-proofing adhesive, a material for laying a railroad, and a fuel. A problem associated with the asphalt, however, is its very poor workability because the viscosity of asphalt is very high at a normal temperature. Accordingly, in order to secure a desired workability of the asphalt at a normal temperature, there has been a technique which converts the asphalt into a workable form, i.e., an oil-in-water asphalt emulsion having a better fluidity, by using an appropriate emulsifier and water.
As for the emulsifiers for use in oil-in-water asphalt emulsions, an anionic emulsifier, a cationic emulsifier, an amphoteric emulsifier, and a nonionic emulsifier are known, and these emulsifiers are used according to respective applications. Among these emulsifiers, the nonionic emulsifier is characterized by its good chemical stability, i.e., good stability to polyvalent metal ions present in water or mingled in the system from outside as well as to other impurities mingled in the system from outside. Because of this, a nonionic emulsifier is suited for the production of a chemically stable asphalt emulsion.
Examples of these nonionic emulsifiers which are generally used are polyoxyethylene nonylphenyl ether and polyoxyethylene octylphenyl ether. Although these nonionic emulsifiers provide the above-mentioned chemical stability, these nonionic emulsifiers do not provide satisfactory stability in a stationary state and storability of the asphalt emulsion because the asphalt emulsion containing such a nonionic emulsifier is not stable when the asphalt emulsion is left to stand for a long period of time.
The technologies hitherto known of asphalt emulsions by use of nonionic emulsifiers are an oil-in-water asphalt emulsion (described in JP-B No. 47-35059) using an asphalt, a nonionic emulsifier, which is prepared by adding either ethylene oxide or propylene oxide and ethylene oxide to an aryloxy or alkylaryloxy group, and water as well as an asphalt emulsion for use as an O/W prime coat (JP-A No. 56-8462) using an asphalt, a hydrocarbon-based or halogenated hydrocarbon-based organic solvent, a cationic emulsifier, a nonionic emulsifier which is prepared by adding ethylene oxide either to an aliphatic alcohol or to an alkylphenol, and water. However, neither of these emulsions is satisfactory with respect to long-term stability in a stationary state and storability.